Obesity and associated diseases constitute a major threat to global public health. In the past decade, it became clear that obesity is associated with chronic inflammation and inflammation and that metabolic responses are closely linked. During the last cycle of our project, we identified c-Jun N-terminal kinase, JNK, as a key player linking inflammatory and metabolic pathways in obesity and causing insulin resistance. We also identified endoplasmic reticulum stress as a trigger for JNK activation and stress responses leading to insulin resistance and type 2 diabetes. Here, we propose to explore the cellular and molecular targets of JNK, determine the role of JNK-3 in metabolic disease, and study the molecular mechanisms of JNK action. Recent studies suggested that macrophages infiltrate adipose tissue and interact with adipocytes, elicit inflammatory responses, and contribute to the development of insulin resistance and type 2 diabetes. Using bone marrow transplantation studies, we will address whether JNK activity in bone marrow-derived cells, including macrophages, contributes to its increased activity in obesity and JNK-mediated insulin resistance and adiposity. We will also explore the impact of bone marrow-derived JNK-1 activity in obesity-related adipose tissue inflammation and inflammatory gene expression. In our earlier studies we have only examined JNK-1 and JNK-2 isoforms. We hypothesize that JNK-3 isoform has a role in systemic metabolic regulation and present preliminary data supporting this hypothesis. We will study the impact of JNK-3 deficiency on obesity and type 2 diabetes and explore the potential synergy between JNK-3 and JNK-1 and JNK-2 isoforms in mice with JNK-3/1 and JNK-3/2-combined deficiency in systemic metabolic homeostasis. We will also explore the molecular mechanisms underlying the activity of JNK and an exciting regulatory loop between JNK activity and XBP-1-mediated ER stress responses. We present preliminary evidence demonstrating a link between JNK and XBP-1, a critical regulator of ER stress responses, and plan to focus on this interaction and examine the significance of this JNK-mediated modification on XBP-1 function. In addition, we will study the biology of, STAMP2, a molecule strongly regulated by TNF in cultured adipocytes and adipose tissue. We will examine the role of STAMP2 in adipose tissue inflammation and systemic insulin action and explore its mechanisms of regulation and action in adipose tissue.